The present invention relates to polycrystalline materials having Single-Crystal-Like properties, in which a plurality of Single-Crystal Particles are assembled together with their crystallographic axes aligned in at least one, but also possibly in two or three dimensions. The present invention also relates to methods for forming the polycrystalline materials of the present.
Single crystal materials have applications in mechanical, electronic, electromechanical, optical and magnetic devices. However, the growth and processing of large single crystals is difficult, time-consuming and expensive. The growth of ceramic single crystals from high temperature melt or liquid solution often require expensive and energy consuming furnaces. The required melt or liquid solution is contained by crucibles often consisting of expensive precious metals such as Pt or Pd. Single crystals must be cooled from their growth temperatures, and can be damaged upon cooling by stresses induced by a variety of factors such as polymorphic phase transformation or anisotropic contraction of the lattice. Stresses can induce cracks or significant changes in crystal properties. These induced stresses can make it difficult, if not impossible, to manufacture useful crystals in large sizes. Other problems associated with high temperature crystal growth arise from phenomena that alter the composition of the crystal such as volatility of one or more of the components and incongruent melting behavior. In addition, molten solvents can introduce impurities into the crystal that cannot be eliminated by conventional purification processes.
Single crystals are typically grown as large boules. These boules are processed by cutting, dicing and polishing prior to incorporation into a device. These steps are time-consuming and may introduce defects. The size of the finished crystal is limited by the processing operation. A lower limit in size of hundreds of microns is typical. The upper size limit is governed by the size and quality of the crystal boule. The size varies greatly with composition. For example, Si can be grown up to a diameter of about 10 inches, while the diameter of YIG may be only on the order of 0.5 inch.
Furthermore, single crystals have lower fracture toughness than their polycrystalline counterparts. Thus, single crystals can be extremely brittle, and their strength can be greatly diminished with surface damage (e.g., scratches) and this diminishes their reliability for many types of applications.
There exists a need for low cost materials with performance properties comparable to single crystals yet which overcome the limitations of single crystals described above and low cost methods for their preparation.